Georgia Perona-Wright

Omega-1, a glycoprotein secreted by Schistosoma mansoni eggs, drives Th2 responses

Soluble egg antigens of the parasitic helminth Schistosoma mansoni (S. mansoni egg antigen [SEA]) induce strong Th2 responses both in vitro and in vivo. However, the specific molecules that prime the development of Th2 responses have not been identified. We report that omega-1, a glycoprotein which is secreted from S. mansoni eggs and present in SEA, is capable of conditioning human monocyte-derived dendritic cells in vitro to drive T helper 2 (Th2) polarization with similar characteristics as whole SEA. Furthermore, using IL-4 dual reporter mice, we show that both natural and recombinant omega-1 alone are sufficient to generate Th2 responses in vivo, even in the absence of IL-4R signaling. Finally, omega-1–depleted SEA displays an impaired capacity for Th2 priming in vitro, but not in vivo, suggesting the existence of additional factors within SEA that can compensate for the omega-1–mediated effects. Collectively, we identify omega-1, a single component of SEA, as a potent inducer of Th2 responses.

Systemic but Not Local Infections Elicit Immunosuppressive IL-10 Production by Natural Killer Cells

Surviving infection represents a balance between the proinflammatory responses needed to eliminate the pathogen, and anti-inflammatory signals limiting damage to the host. IL-10 is a potent immunosuppressive cytokine whose impact is determined by the timing and localization of release. We show that NK cells rapidly express IL-10 during acute infection with diverse rapidly disseminating pathogens. The proinflammatory cytokine IL-12 was necessary and sufficient for NK cell induction of IL-10. NK cells from mice with systemic parasitic infection inhibited dendritic cell release of IL-12 in an IL-10-dependent manner, and NK cell depletion resulted in elevated serum IL-12. These data suggest an innate, negative feedback loop in which IL-12 limits its own production by eliciting IL-10 from NK cells. In contrast to disseminating pathogens, locally restricted infections did not elicit NK cell IL-10. Thus systemic infections uniquely engage NK cells in an IL-10-mediated immunoregulatory circuit that functions to alleviate inflammation.

Signalling by glial cell line-derived neurotrophic factor (GDNF) requires heparan sulphate glycosaminoglycan

Glial cell line-derived neurotrophic factor, GDNF, is vital to the development and maintenance of neural tissues; it promotes survival of sympathetic, parasympathetic and spinal motor neurons during development, protects midbrain dopaminergic neurons from apoptosis well enough to be a promising treatment for Parkinsons disease, and controls renal and testicular development. Understanding how GDNF interacts with its target cells is therefore a priority in several fields. Here we show that GDNF requires glycosaminoglycans as well as the already-known components of its receptor complex, c-Ret and GFRα-1. Without glycosaminoglcyans, specifically heparan sulphate, c-Ret phosphorylation fails and GDNF cannot induce axonogenesis in neurons, in PC-12 cells, or scatter of epithelial cells. Furthermore, exogenous heparan sulphate inhibits rather than assists GDNF signalling. The involvement of heparan sulphates in GDNF signalling raises the possibility that modulation of heparan expression may modulate signalling by GDNF in vivo.

Inflammatory chemokine receptors regulate CD8+ T cell contraction and memory generation following infection

CD8+ T cells lacking CXCR3 and CCR5 expression have impaired contraction and generate an increased number of memory cells after virus infection.

Sustained signaling by canonical helper T cell cytokines throughout the reactive lymph node

Cytokines are soluble proteins that regulate immune responses. The present paradigm is that cytokine production in lymphoid tissues is tightly localized and signaling occurs between conjugate cells. Here we assess cytokine signaling during infection by measuring in vivo phosphorylation of intracellular signal transducer and activator of transcription (STAT) proteins. We show that interferon-γ (IFN-γ) and interleukin 4 (IL-4) signaled to the majority of lymphocytes throughout the reactive lymph node and that IL-4 conditioning of naive, bystander cells was sufficient to override opposing T helper type 1 (TH1) polarization. Our results demonstrate that despite localized production, cytokines can permeate a lymph node and modify the majority of cells therein. Cytokine conditioning of bystander cells could provide a mechanism by which chronic worm infections subvert the host response to subsequent infections or vaccination attempts.

Dendritic Cell Expression of OX40 Ligand Acts as a Costimulatory, Not Polarizing, Signal for Optimal Th2 Priming and Memory Induction In Vivo

Costimulatory cross-talk can occur at multiple cellular levels to potentiate expansion and polarization of Th responses. Although OX40L ligand (OX40L) is thought to play a key role in Th2 development, the critical cellular source of this molecule has yet to be identified. In this study, we demonstrate that OX40L expression by the initiating dendritic cell (DC) is a fundamental requirement for optimal induction of primary and memory Th2 responses in vivo. Analysis of the kinetics of the residual Th2 response primed by OX40L-deficient DC suggested a failure to stimulate appropriate expansion and/or survival of T cells, rather than an inability to polarize per se. The dependence upon OX40L was predominantly due to the provision of signaling through OX40 rather than retrograde signaling to the DC. Mechanistically, impaired Th2 priming in the absence of OX40L was not due to exaggerated regulation because there was no evidence of increased expansion or function of regulatory cell populations, suppression through IL-10 production, or hyporesponsiveness to secondary challenge. These data define a critical role for DC-derived OX40L in the induction and development of Th2 responses in vivo.

Anti-CD25 antibody-mediated depletion of effector T cell populations enhances susceptibility of mice to acute but not chronic Toxoplasma gondii infection

Natural regulatory T cells (Tregs) constitutively express the IL-2R α-chain (CD25) on their surface. Consequently, administration of anti-CD25 Abs is a commonly used technique to deplete Treg populations in vivo. However, activated effector T cells may also transiently express CD25, and are thus also potential targets for anti-CD25 Abs. In this study using Toxoplasma gondii as a model proinflammatory infection, we have examined the capacity of anti-CD25 Abs to target effector T cell populations during an inflammatory episode, to determine to what extent that this action may modulate the outcome of disease. Anti-CD25 Ab-treated C57BL/6 mice displayed significantly reduced CD4+ T cell IFN-γ production during acute T. gondii infection and exhibited reduced weight loss and liver pathology during early acute infection; aspects of infection previously associated with effector CD4+ T cell responses. In agreement, anti-CD25 Ab administration impaired parasite control and caused mice to succumb to infection during late acute/early chronic stages of infection with elevated tissue parasite burdens. In contrast, anti-CD25 Ab treatment of mice with established chronic infections did not markedly affect brain parasite burdens, suggesting that protective T cell populations do not express CD25 during chronic stages of T. gondii infection. In summary, we have demonstrated that anti-CD25 Abs may directly abrogate effector T cell responses during an inflammatory episode, highlighting important limitations of the use of anti-CD25 Ab administration to examine Treg function during inflammatory settings.

Perinatal antibiotic-induced shifts in gut microbiota have differential effects on inflammatory lung diseases.

BACKGROUND Resident gut microbiota are now recognized as potent modifiers of host immune responses in various scenarios. Recently, we demonstrated that perinatal exposure to vancomycin, but not streptomycin, profoundly alters gut microbiota and enhances susceptibility to a TH2 model of allergic asthma. OBJECTIVE Here we sought to further clarify the etiology of these changes by determining whether perinatal antibiotic treatment has a similar effect on the TH1/TH17-mediated lung disease, hypersensitivity pneumonitis. METHODS Hypersensitivity pneumonitis was induced in C57BL/6 wild-type or recombination-activating gene 1-deficient mice treated perinatally with vancomycin or streptomycin by repeated intranasal administration of Saccharopolyspora rectivirgula antigen. Disease severity was assessed by measuring lung inflammation, pathology, cytokine responses, and serum antibodies. Microbial community analyses were performed on stool samples via 16S ribosomal RNA pyrosequencing and correlations between disease severity and specific bacterial taxa were identified. RESULTS Surprisingly, in contrast to our findings in an allergic asthma model, we found that the severity of hypersensitivity pneumonitis was unaffected by vancomycin, but increased dramatically after streptomycin treatment. This likely reflects an effect on the adaptive, rather than innate, immune response because the effects of streptomycin were not observed during the early phases of disease and were abrogated in recombination-activating gene 1-deficient mice. Interestingly, Bacteroidetes dominated the intestinal microbiota of streptomycin-treated animals, while vancomycin promoted the expansion of the Firmicutes. CONCLUSIONS Perinatal antibiotics exert highly selective effects on resident gut flora, which, in turn, lead to very specific alterations in susceptibility to TH2- or TH1/TH17-driven lung inflammatory disease.

A Pivotal Role for CD40-Mediated IL-6 Production by Dendritic Cells during IL-17 Induction In Vivo

The costimulatory requirements for Th17 development remain to be defined. In this study, we show that CD40-deficient animals immunized with the Gram-positive bacterium Propionibacterium acnes were specifically impaired in their ability to mount an IL-17 response, but not that of IFN-γ. The same cytokine imbalance resulted from in vivo priming with pathogen-pulsed, CD40-deficient dendritic cells (DC). Engagement of CD40 on P. acnes-conditioned DC stimulated the release of IL-12, IL-23, and IL-6, of which IL-6 alone proved essential for Th17 differentiation. Compared with wild-type DC, priming with those lacking expression of CD40 resulted in reduced disease severity during experimental autoimmune encephalomyelitis, coincident with reduced IL-17 production. Our data delineate sequential requirements for DC expression of CD40 and production of IL-6 during Th17 polarization in vitro and in vivo, and reveal distinct costimulatory requirements for Th1 vs Th17 generation.

The role of ICOS in the development of CD4 T cell help and the reactivation of memory T cells

We have addressed the role of the inducible costimulator (ICOS) in the development of T cell help for B cells and in the generation, survival and reactivation of memory CD4 T cells and B cells. We find that while T cell help for all antibody isotypes (including IgG2c) is impaired in ICOS knockout (ICOS‐KO) mice, the IFN‐γ response is little affected, indicating a defect in helper function that is unrelated to cytokine production. In addition, the ICOS‐negative T cells do not accumulate in B cell follicles. Secondary (memory), but not primary, clonal proliferation of antigen‐specific B cells is impaired in ICOS‐KO mice, as is the generation of secondary antibody‐secreting cells. Analysis of endogenous CD4 memory cells in ICOS‐KO mice, using MHC class II tetramers, reveals normal primary clonal expansion, formation of memory clones and long‐term (10 wk) survival of memory cells, but defective expansion upon reactivation in vivo. The data point to a role of ICOS in supporting secondary, memory and effector T cell responses, possibly by influencing cell survival. The data also highlight differences in ICOS dependency of endogenous T cell proliferation in vivo compared to that of adoptively transferred TCR‐transgenic T cells.